Abstract
Abstract. The anthropogenic increase of carbon dioxide (CO2) alters the seawater carbonate chemistry, with a decline of pH and an increase in the partial pressure of CO2 (pCO2). Although bacteria play a major role in carbon cycling, little is known about the impact of rising pCO2 on bacterial carbon metabolism, especially for natural bacterial communities. In this study, we investigated the effect of rising pCO2 on bacterial production (BP), bacterial respiration (BR) and bacterial carbon metabolism during a mesocosm experiment performed in Kongsfjorden (Svalbard) in 2010. Nine mesocosms with pCO2 levels ranging from ca. 180 to 1400 μatm were deployed in the fjord and monitored for 30 days. Generally BP gradually decreased in all mesocosms in an initial phase, showed a large (3.6-fold average) but temporary increase on day 10, and increased slightly after inorganic nutrient addition. Over the wide range of pCO2 investigated, the patterns in BP and growth rate of bulk and free-living communities were generally similar over time. However, BP of the bulk community significantly decreased with increasing pCO2 after nutrient addition (day 14). In addition, increasing pCO2 enhanced the leucine to thymidine (Leu : TdR) ratio at the end of experiment, suggesting that pCO2 may alter the growth balance of bacteria. Stepwise multiple regression analysis suggests that multiple factors, including pCO2, explained the changes of BP, growth rate and Leu : TdR ratio at the end of the experiment. In contrast to BP, no clear trend and effect of changes of pCO2 was observed for BR, bacterial carbon demand and bacterial growth efficiency. Overall, the results suggest that changes in pCO2 potentially influence bacterial production, growth rate and growth balance rather than the conversion of dissolved organic matter into CO2.
Highlights
Bacteria are the main organisSmos tlhidat iEncaorrptohrate and mineralise dissolved organic carbon in the ocean, recycling about50 % of daily primary production
Previous studies have examined the effect of pressure of CO2 (pCO2) on microbial communities and found that pCO2 potentially alters bacterial production (BP) (Coffin et al, 2004; Grossart et al, 2006; Yamada et al, 2010), growth rate (Grossart et al, 2006), enzymatic activity (Grossart et al, 2006; Piontek et al, 2010; Yamada and Suzumura, 2010) and community structure (Allgaier et al, 2008; Yamada et al, 2010); whereas little or no effect of pCO2 was found for BP (Allgaier et al, 2008; Arnosti et al, 2011) and abundance (Rochelle-Newall et al, 2004; Grossart et al, 2006; Allgaier et al, 2008; Arnosti et al, 2011) or chromophoric dissolved organic matter (Rochelle-Newall et al, 2004)
There is no study on the effect of pCO2 on specific carbon metabolism components such as bacterial respiration (BR), Bacterial growth efficiency (BGE) and bacterial carbon demand (BCD) of natural bacterial communities in aquatic environments
Summary
Bacteria are the main organisSmos tlhidat iEncaorrptohrate and mineralise dissolved organic carbon in the ocean, recycling about50 % of daily primary production. A recent review paper suggests that unlike calcifying organisms, the effect of pCO2 on biogeochemical processes driven by microbes or microbial function in the oceans might be minor (Joint et al, 2011). This has been challenged by Liu et al (2010). There is no study on the effect of pCO2 on specific carbon metabolism components such as BR, BGE and BCD of natural bacterial communities in aquatic environments
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